For setting the iris diaphragm opening, picture definition and focal width of a camera lens, lens rings are mounted on the lens housing. By turning the lens rings, the lens system is linearly displaced through a gearing and, thus, the picture definition and focal width of the camera lens are changed. The manual adjustment of the iris diaphragm opening, focus and focal width (zoom) of the camera lens on the lens rings provided for this purpose is difficult for the cameraman. This is particularly difficult when viewing, at the same time, the image through the viewfinder eyepiece. Making reproducible setting of certain focal widths, focus values and iris diaphragm openings is linked with considerable difficulties and, further, pre-programming predeterminable values is not possible.
For a simpler and more reliable setting of the lens rings, drive units are known which are fixed on iris rods connected to the camera housing and each transferring, through a pinion, a torque to an external gearing of the lens rings so as to carry out the adjustment of the lens rings in this way. With these additional drive units, the operation is easier for the cameraman and there is the possibility of connecting the drive units to a control device or to set pre-programmable values for the iris diaphragm opening, the image definition and focal width of the camera lens.
Converting the rotary movement of the lens rings into the linear displacement of the lens system of the camera lens requires, however, a certain play in order to allow easy adjustability. In the same way, a certain play between the pinion of the drive unit and the external teething of the lens ring is unavoidable, which is a problem particularly when focusing where the slightest displacements of the camera lens can lead to the image being out of focus. Less of a problem is setting the iris diaphragm opening and the focal width, because the image detail and the depth of focus can be easily corrected and even slightly inaccurate settings need not lead to the shots becoming unusable.
In many cases the use of an optically optimized lens with fixed focal width is possible wherein only the adjustment of the iris diaphragm opening and image definition is required.
From U.S. Pat. No. 4,437,552, a movie film camera is known having a shutter, film transport mechanism and a focusing device which are driven by a common drive motor through a spring coupling. The camera lens is connected to a displacement device for the translatory displacement of the camera lens. The device consists of a connecting rod which is mounted in fixed guides and is connected to a cam disc. The cam disc controls the translation movement of the camera lens and is connected to a worm gear connected to the spring coupling. The displacement device is additionally connected to a device for automatically focusing the film pictures.
From U.S. Pat. No. 3,250,197 a focusing device for an image converter connected to a picture carrier is known which consists of a device for the translatory displacement of the distance between a lens assembly connected to the image converter and the picture carrier.
From DE A 342 40 14 a stationary film camera is known wherein to focus the picture it is not the lens, but the film gate with the film window which is moved in translation along the optical axis of the stationary film camera. The translatory displacement is undertaken by several spindles set parallel to the optical axis and engaging in threaded bores of the film gate. Through a synchronous turning of the spindles, the film gate is moved in translation in the direction of the optical axis until, in dependence on an automatic distance meter, an electromagnetically operated locking means drops into the gearing. After film exposure and during the next film transport step, the gearing is returned with the film gate back to the starting position.